docs: def actions(self, state):
          '''Returns a list of the pieces we can move to the empty space.'''
          rows = string_to_list(state)
          row_e, col_e = find_location(rows, 'e')
  
          actions = []
          if row_e > 0:
              actions.append(rows[row_e - 1][col_e])
          if row_e < 2:
              actions.append(rows[row_e + 1][col_e])
          if col_e > 0:
              actions.append(rows[row_e][col_e - 1])
          if col_e < 2:
              actions.append(rows[row_e][col_e + 1])
  
          return actions